The recovery and purification of argon for use in the metallurgical and electronics industries is an important aspect of the air separation industry. Argon is recovered by the well-known process of cryogenic air separation using a double distillation column of the Linde type with an argon sidearm column to recover crude argon from a low pressure column sidestream. This process is described by R. E. Latimer in an article entitled "Distillation of Air" in Chemical Engineering Progress, 63(2), 35-59 (1967), and typically produces a crude argon product containing between 2 and 5 mol % oxygen and less than 1mol % nitrogen. Since argon is a valuable product, it is desirable to maximize its recovery at acceptable purity levels. With currently practiced process technology, crude argon containing less than about 2.0 mol % oxygen can be produced only by reducing recovery to generally unacceptable levels. This relationship between recovery and purity in current process technology is well known and is described in the textbook entitled "Separation of Gases" by M. Ruhemann, Second Edition, Oxford University press, 1949, at page 223.
Soviet Patent Application No. SU 1416820 A discloses a two-zone argon sidearm column to increase argon purity at an acceptable recovery in which a first zone contains a number of sieve trays such that the pressure at the top of the zone is near atmospheric. The gas from the top of this zone is warmed, compressed, cooled, and fed to the lower part of a second zone, and a crude argon stream containing a reduced concentration of oxygen is withdrawn from the top of this second zone. Additional heat exchange and compression equipment is required to accomplish this improved argon purity.
The removal of oxygen from typical crude argon streams containing 2 to 5 mol % oxygen is commonly accomplished by catalytic reaction with hydrogen over a platinum or palladium catalyst to yield water. The argon is then dried and cooled to cryogenic temperature for removal of residual hydrogen and other impurities by distillation. A large recycle stream (about 1:1 recycle:crude argon) of ambient temperature deoxygenated argon is combined with the crude argon feed to the catalytic reactor to control the reactor exotherm at a safe level. This is required because the high heat of reaction with a feed containing 2-5 mol % oxygen can cause overheating of the reactor. A compressor or blower is required for this recycle. In addition, excess hydrogen is required to ensure satisfactory oxygen removal, and the removal of hydrogen from the cooled and dried reactor effluent requires additional trays in the distillation column for final argon purification. A high purity argon product containing less than 5 ppmv oxygen is obtained by this well-known method.
European Patent Office Publication No. 0 331 028 Al discloses a method for the recovery of high purity argon at a purity of 99.999 vol % from crude argon containing 90 to 99 vol % argon in which a vapor and a liquid crude argon stream are taken overhead from an argon sidearm column and are warmed and vaporized respectively. The warmed vapor is combined with an oxygen-free argon recycle stream, is compressed, and is combined with the vaporized crude argon stream; the combined argon stream is mixed with a hydrogen-containing stream and passed through a catalytic reactor in which oxygen combines with hydrogen to form water. The water is removed in a drier and the resulting argon stream is purified in a final distillation step to yield high purity argon product.
Oxygen can be removed from argon and other inert gases by gettering in which the oxygen is reacted with one or more reduced metals typically supported on a catalyst substrate and packed into a reactor vessel. U.S. Pat. No. 3,697,445 and British Patent No. 1,263,132 disclose a high surface area nickel getter catalyst containing 25 to 50 wt % nickel on silica for the removal of oxygen from inert gases at ambient temperatures or below. The catalyst can be used to remove oxygen to less than about 0.2 ppmv and can be regenerated by reduction with hydrogen at 200.degree.-500.degree. C.
A catalyst for oxygen removal containing 30 wt % copper on a carrier substrate is described in a Technical Leaflet on Catalyst R3-11 by BASF Corporation. The catalyst can be used to remove oxygen from inert gases by gettering at temperatures up to 250.degree. C., and the catalyst can be regenerated by reduction with hydrogen. When oxygen concentrations are above about 0.5-2.0 mol %, the feed must be diluted to hold the temperature below 250.degree. C., or a special high temperature catalyst must be used.
A one-step process for the removal of an impurity selected from oxygen, CO, CO.sub.2, hydrogen, water, or mixtures thereof at less than 1000 ppmv in an inert gas is disclosed in U.S. Pat. No. 4,713,224. The gas is passed over a catalyst comprising at least 5 wt % nickel at a temperature between 0.degree. and 50.degree. C. and a product containing less than several ppmv impurities is obtained. The catalyst is regenerated by purging with nitrogen and hydrogen at 180.degree. to 200.degree. C.
French Patent Application No. 84 00096 discloses the removal of impurities comprising oxygen and other components from noble gases by contacting the gas with porous pellets of a titanium-zirconium alloy at temperatures between 400.degree. and 900.degree. C. The alloy can be regenerated after saturation by applying a vacuum or a reducing atmosphere.
U.S.S.R. Patent Application No. 2,995,864/23-26 discloses the removal of oxygen impurity from an inert gas by contacting the gas at room temperature with a reduced form of a catalyst containing oxides of chromium, zinc, aluminum, and copper. Spent catalyst is regenerated by contacting with a reducing nitrogen-hydrogen mixture.
The removal of oxygen from an inert gas by contacting with a well-reduced nickel catalyst at room temperature is disclosed in Japanese Patent Application No. 45-123711. Methods for the preparation of the catalyst are disclosed and its regeneration by contacting with hydrogen at between 30.degree. and 200.degree. C. is described.
In an article entitled "Catalytic and Adsorption Chemical Treatment for Removing Oxygen from Inert Gases, Hydrogen, and Methane" in Khim. Prom-st (Moscow) (6), 373-4, A. S. Barabash et al describe the removal of oxygen from inert and other gases by contacting with a nickel/Cr.sub.2 O.sub.3 adsorbent at between 20.degree. and 200.degree. C. Oxidized nickel is reduced with hydrogen at 280.degree. C. for further oxygen removal.
Japanese Patent Publication No. 62(1987)-22,923 discloses method for the removal of oxygen from an inert gas by adding hydrogen to the inert gas, passing the gas over a palladium catalyst to convert most of the oxygen to water, and then passing the gas over a copper and/or nickel catalyst which removes residual oxygen by gettering. When the catalyst nears exhaustion, a controlled amount of hydrogen is added to the gas flowing to the copper and/or nickel catalyst which is then regenerated. The water in the final product is removed by drying if necessary.
U.S. Pat. No. 3,535,074 describes a method and appartus for removing oxygen from an inert gas by adding excess hydrogen to the gas, passing the gas over a catalyst containing a platinum-group metal, and then passing the gas over a copper and/or nickel catalyst to remove residual oxygen. The copper and/or nickel catalyst serves as a guard in the event that the feed gas contains a increased amount of oxygen. Excess hydrogen and water are then removed from the final product.
The removal of parts per million levels of impurities such as oxygen, CO, CO.sub.2, hydrogen, and water from an inert gas stream is disclosed in U.S. Pat. No. 4,579,723. The gas is passed initially through a first bed of catalyst containing chromium and platinum in which CO reacts with oxygen to form CO.sub.2, and hydrogen reacts with oxygen to form water at ambient temperature. The gas then is passed through a second bed of catalyst containing a getter comprising copper, nickel, and cobalt, which removes oxygen and traps CO.sub.2. Water is generally retained in the first bed, and alumina can be added to the first bed if the water concentration in the feed inert gas is above a predetermined level.